In the recent past, wireless sensors have found their way into a wide variety of applications and systems with vastly varying requirements and characteristics. Wireless sensors offer a powerful combination of distributed sensing, computing and communication. They lend themselves to countless applications and, at the same time, offer numerous challenges due to their peculiarities, primarily the stringent energy constraints to which wireless sensors are typically subjected. The distinguishing traits of wireless sensors have a direct impact on the hardware and algorithm design at four levels: power source, hardware, accuracy of detection, and speed of protection.
Automatic detection and prevention of certain accidents is but one of many potential applications of wireless sensors. Wireless sensors have captured the attention and imagination of many researchers, encompassing a broad spectrum of the ideas. Despite their variety, all wireless sensors have certain fundamental features in common. Perhaps most essential is that they are embedded in the real world. Wireless sensors detect the world's physical nature, such as surrounding objects, their proximity, their distance and speed. Similarly, actuators affect the world in some way, such as activating a device, making a noise, or exerting a force. Such a close relationship with physical world is a dramatic contrast to much of traditional computing, which often exist in virtual world.
Smart environments represent the next evolutionary development step in building, utilities, industrial, home, shipboard, and transportation systems automation. Like any sentient organism, the smart environment relies first and foremost on sensory data from the real world. Sensory data comes from multiple sensors of different modalities in distributed locations. The smart environment needs information about its surroundings as well as about its internal workings.
Wireless sensors are standard measurement tools equipped with transceiver to convert signals from a control processor into a radio transmission and then receive the reflected signal by a receiver which then detects the received signal and sends it to a processor to be analyzed. There are a number of items to consider when selecting a wireless measurement instrument.
Type of Measurement:
It is important to understand what is being measured. Wireless transceivers sensor (which incorporate wireless process measurement and control) typically have a unique function. Sensors are specifically designed for speed, distance, flow, etc., and must be selected accordingly.
Accuracy and Response Time:
How accurate does the measurement need to be, and how quickly should the measurement be updated? Most wireless sensors are as accurate as their wired counterparts; however a signal is typically transmitted frequent enough to allow for accurate measurement while preserving battery power.
Range:
The range of wireless sensors varies widely. Some are designed for short-range of a few feet, while other sensors can cover few hundred feet. Regardless of the sensors capability, the range of a wireless signal is always limited by signal bandwidth, and frequency of operation. For certain applications very high operating frequency has to be used which limit the operation range.
Frequency:
The frequency of radio transmission is also important to consider. Laws vary by country and region as to which parts of the wireless spectrum are available for use without specific licenses. Accuracy and response time in certain application depends on operating frequency, the higher the frequency the more accurate the measurement of certain parameters.
Various components of a wireless sensor system are;
Transmitters:
In certain applications the transmitters use particular signals to send via radio waves to a receiver.
Receiver:
receives and interpret the wireless data. The receiver ‘reads’ a radio signal, utilize it to estimate and calculate certain parameters, and then send them to a controller to make decision.
Controller:
receives and analyze data from wireless receiver. However, the wireless controller is also able to manipulate a process based on the data being measured.
The drawings referred to in this description should be understood as not being drawn to scale except if specifically noted.